since recently (~2 weeks) I noticed the pkd process maxing out available CPU time after LaunchBar v6.8 (6140) has been running for some time. Quitting and relaunching LaunchBar immediately solves the problem until it starts again after a while. I am running Mac OS Sierra, 10.12.3 (16D32).
Your release notes mention for v6.4.1 (6121)
Fixed: The actions indexing rule was continuously re-indexed because the OS X Action Extensions seemed to have changed (this resulted in high CPU usage by LaunchBar and “pkd”).
Any chance this has come back?